This study involves the use of investigational vaccines. A vaccine is a medicine that causes the body to make antibodies. Antibodies help destroy foreign substances that enter the body. The purpose of this study is to find the right dose of a new vaccine that is safe and produces a good immune response (how well your body recognizes and defends itself against harmful foreign substances). There are two Staphylococcus aureus toxoids (components or antigens) under investigation in this study; one of them is a protein known as rAT and the other is a protein known as rLukS-PV. They are being developed to see if they are effective at preventing infections caused by the bacteria Staphylococcus aureus.